<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>案例</title>
</head>
<body>
  用户名: <input type="text" id="username">
  <p></p>
</body>
<script>
  //获取input元素
  const input = document.querySelector('input') 
  const p = document.querySelector('p')
  //声明handle函数
  function handle(data){
    input.style.border="1px solid orange";
    p.innerHTML = data.msg
  }

  //绑定事件
  input.onblur = function(){
    //获取用户的输入
    let username = this.value
    //向服务器端发送请求，检测用户名是否存在
    //1.创建一个script标签
    const script= document.createElement('script')
    //2.设置标签的src属性
    script.src = 'http://127.0.0.1:8000/check-username'
    //3.将script插入到文档中
    document.body.appendChild(script)
}
</script>
</html>